1. Field of the Invention
The invention in general relates to the field of implantable connectors for making physical and electrical connection to an implantable lead and, more particularly, concerns an improved connector with a dynamic gripping action that permits a positive connection without the use of set screws, adhesives, etc.
2. Description of the Prior Art
In recent years many devices have been developed which are designed for implantation in a body. For example, electrical tissue stimulators are now routinely implanted in humans for treatment of heart block, pain, scoliosis, and other medical problems. Generally an electrical lead is used with these devices to carry an electrical current or voltage from a pulse generator or other electrical device to the body part that needs to be treated. Such leads generally consist of a conductor encased in an insulator which is generally inert to body fluids. In many such leads the conductor is in the form of a coil, with a passage down the center of the coil called a lumen. In some cases, it is necessary that several different types of the leads need to be used in order to effectively deliver the electrical voltage or current to the appropriate portion of the body. For example, when stimulating the spinal cord it is necessary to use a very thin lead over the portion of the conductive path which passes through the epidural space, while in the portion of the electrical path which passes through muscle and surface tissue it is desirable to use a lead that is thicker and stronger and thus more resistant to breakage. Connectors are generally used to make the physical and electrical connection between the two portions of the lead in such a situation. Connectors are also used in connecting the lead to the terminal of the electrical device which produces the current or voltage.
Conventional electrical connectors used in external applications generally are not suitable for use with implanted devices. Implanted devices must be highly reliable because patients' health and life may depend on them for long periods, such as ten years or more, and because they cannot be replaced except by expensive and traumatic surgical procedures. In addition, such devices must be capable of such high reliability in a hostile environment--the human body--in which they are subject to much movement and flexing. For these reasons, up to now, such connectors have consisted of relatively complex positive fixation devices encased in protective materials. Perhaps most common of such devices has been a pin and socket-type arrangement containing a set screw in the socket which can be screwed down upon the pin after the pin is inserted to positively hold the pin in place, with the whole encased in protective medical-grade silicone or similar material. Such connectors tend to be significantly larger than the lead itself and thus add significant bulk to the implantable lead. The larger the implanted device the more trauma it may cause to the body and, thus it is desirable to have smaller connectors. One solution to this problem has been the use of medical adhesive to hold a pin and socket device together. While the use of the medical adhesive may solve some of the bulk problem it has its own disadvantages, such as difficulty in making a disconnection without destroying the part if a disconnection is necessary, contamination of the site due to particles which may become loose, failure of the adhesive under flexing, etc.
Conventional implantable electrical connectors have up to now required special fittings on the lead or other terminal which is to be connected to, in order to ensure a positive fixation. Thus leads must be specially made in fixed lengths with the fittings attached. Since human bodies are of various sizes this results in the necessity of stocking many different lengths of leads, which is expensive and impractical, or the implanting of leads that are longer than necessary and the coiling of the excess length within the body. The excess length adds further bulk to the implanted material and provides additional opportunities for failure and trauma due to the presence and flexing of the superfluous lead length.